1. Field of the Invention
This invention relates to an ohmic electrode, its fabricating method and a light emitting device, and more particularly, to an ohmic electrode onto a p-type II-VI compound semiconductor of p-type ZnTe or the like, its fabricating method, and a light emitting device using the ohmic electrode as its p-side electrode.
2. Description of the Related Art
In recent years, there are active trials for realizing light emitting devices capable of emitting blue to green light, by using a II-VI compound semiconductor of ZnSe or the like. Regarding such light emitting devices using a II-VI compound semiconductor, attention has been paid to that ZnTe which can obtain a p-type crystal having a relatively high carrier concentration is used as a contact layer (also called a cap layer) of a p-side electrode (Japanese Laid Open Patent Publication No. 122565/1990).
In general, Au or Ag is used as a material of the ohmic electrode onto the p-type ZnTe (for example, Semiconductor Handbook (Second Edition), Ohm-sha Limited., p.157.). In lieu of Au or Ag, Pt having a large work function may be used.
There is a description of an Au/Pd electrode provided on a p-type ZnSe in ELECTRONICS LETTER 10th September 1992, Vol. 28, No. 19, pp. 1798-1799. However, no good ohmic characteristic has been obtained.
Since the metals, Au, Ag and Pt, are not reliable in terms of adhesion to p-type ZnTe, and subjected to exfoliation, it is difficult to execute lift-off, cleavage or other processes after depositing such a metal by vacuum evaporation. Further, because of the liability to exfoliation, devices using such metals are not reliable.
The adhesion would be improved by making Au or Ag contact with p-type ZnTe via a Ti film which is widely used to improve adhesion of an ohmic electrode to III-V compound semiconductor. However, it has been recognized through experiments of the present Inventors that the use of a Ti film deteriorates the ohmic characteristic of the electrode.